JPH11254107A - Casting method of ferritic stainless steel molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting method of a molten ferritic stainless steel which prevents the occurrence of ridging without lowering the quality caused by inclusion in a cast slab ans also, without exerting the adverse effect to the quality, such as lowering of the corrosion resistance, by fining down the solidified structure in the cast slab. SOLUTION: Into the molten ferritic stainless steel 10 containing 10-30 wt.% chromium, metallic Mg or Mg alloy is added and Mg % based on the oxygen content (T.O) in the molten ferritic stainless steel 10 is regulated to in the range of the following inequality and the casting is executed. 3/8×(T.O)<=(Mg %)<=5×(T.O)+0.05.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting molten ferritic stainless steel which prevents ridging which occurs when a cast slab is subjected to secondary processing such as pressing on a rolled steel plate.

[0002]

2. Description of the Related Art Ferritic stainless steel sheets are widely used in kitchen appliances and home electric appliances because they have excellent corrosion resistance, maintain beautiful luster for a long period of time, and are relatively inexpensive. This ferritic stainless steel sheet is produced by melting molten steel containing chromium using a converter or an electric furnace, performing vacuum refining, and then rolling a slab obtained by continuous casting or ingot casting. In this way, a thin steel plate is manufactured and subjected to secondary processing such as press forming. However, when secondary processing such as press forming is performed on ferritic stainless steel sheet, it is known that surface defects such as fine irregularities (wrinkles) due to deformation of each crystal grain called ridging occur. Is severe, it not only impairs the appearance of the surface but also causes micro-cracks, so it must be removed by means such as polishing. It is also known that this ridging occurs when the crystal structure of the slab is large. As shown in FIG. 3, the crystal structure of a general slab is a relatively small crystal structure in a chill crystal 30 which is first solidified by primary cooling of a mold, but the cooling is slow inside and a large dendrite 3 is formed inside.
1 crystal structure. This crystal structure also increases as the crystal structure of the steel sheet during and after rolling, and during secondary processing such as press forming, a difference in elongation for each crystal grain is generated, and fine surface irregularities ( Wrinkles). In addition, ridging is remarkably generated in a ferritic stainless steel sheet having no phase transformation and a large crystal structure as compared with an austenitic stainless steel sheet. As a method for preventing this ridging, as disclosed in JP-A-7-15137, Ni oxides, Ti oxides, and other carbides that do not dissolve when added to molten steel are added in a range of 5% by weight or less. , Forming a fine crystalline structure, or "iron and steel (4-S
79)), a method of forming a fine crystal structure by adding a nitride-forming element to form a nitride has been proposed. Further, as a commonly used method for refining the crystal structure, low-temperature casting or electromagnetic stirring is performed to suppress the growth of columnar crystals to form equiaxed crystals.

[0003]

However, in the method of forming a fine crystal structure by adding Ni oxides, Ti oxides, other carbides and the like insoluble in molten steel in a range of 5% by weight or less, the Ni oxide , Oxides of Ti, carbides, etc. do not dissolve in the molten steel, making it difficult to uniformly disperse them throughout the molten steel, causing the additives to agglomerate, lowering the efficiency of forming a fine crystal structure, and agglomerating the additives. The material becomes flawed during rolling.
Furthermore, in order to prevent the aggregation of the additives, special measures are required for the addition method, but there is a problem that there is no specific means and there is no possibility of realization. In a method of forming a fine crystal structure by adding a nitride-forming element to form a nitride, for example, when adding Ti, 0.15% by weight or more is added. It is necessary, and there are problems such as an increase in inclusions, an adverse effect on the material such as a decrease in corrosion resistance, and an increase in alloy cost. Further, even in a commonly used method for refining a crystal structure, the efficiency of forming a fine crystal structure is low. Particularly, in low-temperature casting, there is a problem in casting such as nozzle clogging and metal adhesion due to low temperature. There are problems such as.

[0004] The present invention has been made in view of the above circumstances, by preventing the occurrence of ridging by minimizing the solidification structure of the slab, to reduce the quality and corrosion resistance of the slab due to inclusions in the slab. It is an object of the present invention to provide a method of casting molten ferritic stainless steel that has little adverse effect on steel.

[0005]

According to the present invention, there is provided a semiconductor device comprising:
The casting method of the molten ferritic stainless steel described in the above is to add a metal Mg or an Mg alloy to a molten ferritic stainless steel containing 10 to 30% by weight of chromium, and to set Mg% to the oxygen content of the molten ferritic stainless steel as follows. The casting is performed within the range of the equation (1). 3/8 × (TO) ≦ (Mg%) ≦ 5 × (TO) +0.05 (1) O is the total oxygen content in molten ferritic stainless steel (% by weight) Mg is the Mg content in molten ferritic stainless steel (% by weight) Here, the chromium content of the molten ferritic stainless steel is 10% by weight. If the amount is less, the corrosion resistance of the product decreases. On the other hand, if the chromium content is more than 30% by weight, a large amount of expensive alloy is used and the cost is greatly increased, but the corrosion resistance of the product is not so improved. On the other hand, when the content of Mg is less than 3/8 × (TO), the absolute amount of inoculation nuclei generated in the molten ferritic stainless steel is insufficient, and the crystal structure of the solidified slab is refined. Can not. If the Mg content exceeds 5 × (TO) +0.05, the effect of miniaturization is saturated, and the cost of the added metallic Mg or the like increases.

According to a second aspect of the present invention, there is provided a method for casting a molten ferritic stainless steel according to the first aspect, wherein the molten ferritic stainless steel is deoxidized with Al or an Al alloy.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. FIG. 1 is a schematic view of a continuous casting apparatus used in a method for casting molten ferritic stainless steel according to an embodiment of the present invention, and FIG. 2 is a solidification structure diagram of a cross section of a slab. As shown in FIG. 1, a continuous casting apparatus A pours a molten ferritic stainless steel (hereinafter, referred to as molten steel) 10 into a mold 13 from an immersion nozzle 12 provided in a tundish 11, and performs primary cooling by the mold 13 to solidify the solidified shell. Is formed, the slab 15 is subsequently supported by the support segments 14, and water is sprayed from a cooling water nozzle (not shown) to promote solidification. Further, the slab 15 is lowered by a predetermined pushing amount by the pressing segment 16, continuously pulled out by the pinch roll 17, cut into a predetermined size,
Rolled.

Next, a method of casting molten ferritic stainless steel according to one embodiment of the present invention using the continuous casting apparatus A will be described. The molten steel 10 is prepared by adding a chromium alloy in a converter or an electric furnace or the like, decarbonizing and refining C to about 0.60% by weight, and then performing vacuum secondary refining (not shown).
Is adjusted to 0.050% by weight and Cr to 10.0% by weight, and contains Si, Mn and the like as necessary. The molten steel 10 is provided with a dipping nozzle 12 provided in a tundish 11.
Is poured into a mold 13 and solidified into a slab 15 by primary cooling by the mold 13 and water spraying from a cooling water nozzle (not shown) attached to the support segment 14. The slab 15 was continuously drawn by a pinch roll 17 at a predetermined casting speed (m / min). Further, when the slab 15 is pulled out by the pinch roll 17, a reduction corresponding to a pressing amount of 5 to 10 mm is performed by the reduction segment 16, and internal defects such as center porosity formed inside are pressed. In addition, molten steel 10
Is free oxygen and FeO, SiO in the process of melting by a converter, an electric furnace or a vacuum secondary refining (not shown).
₂ , oxides such as MnO and Al ₂ O ₃ , and the total oxygen content (TO) of these oxides was adjusted to 0.0025% by weight by adjusting the deoxidizing agent. Then, particles of metallic Mg are added to the molten steel 10 in the tundish 11 so that the M
g% is 3/8 × (TO) to 5 × (TO) +0.05
It was added so as to be in the range of 0.0009 to 0.0625% by weight corresponding to the value.

The added metallic Mg reacts with oxygen and oxides contained in the molten steel 10 to produce MgO,
O is dispersed in the molten steel 10. When the molten steel 10 is cooled and solidified in the mold 13 and the support segment 14, the MgO lattice constant of 0.4213 nm (nanometer) is very close to the lattice constant of δ-iron of 0.4054 nm (nanometer). Therefore, it acts as an inoculation nucleus (from which the molten steel solidifies first). As a result, M
Solidification starts with gO as a nucleus and subsequently grows into crystal grains. Then, when the adjacent crystal grains come into contact with each other, the growth of the crystal grains stops. Therefore, the more the MgO is dispersed in the molten steel 10, the smaller the crystal grains become, and the finer the crystal structure can be. However, if the oxygen content (TO) in the molten steel 10 is extremely small with respect to the added metallic Mg, a part of the metallic Mg forms MgO, and the others tend to be present in the molten steel 10 as Mg. Show. Further, MgO is a MgO · Al ₂ O ₃ easily formed by reacting, Al ₂ O _3, based on mixed in the molten steel 10, this MgO · Al ₂ O ₃ acts as an inoculum nucleus. For this reason, when the Mg concentration is lower than 3/8 × (TO), the absolute amount of the inoculation nucleus becomes insufficient, and Al ₂ O ₃ mixed in the molten steel is used to minimize the use of oxygen. can not form had been inoculated nuclei (MgO · Al ₂ O _3), since the MgO serving as inoculation nuclei (MgO · Al ₂ O ₃₎ amount is insufficient, not be fine crystal structure of the solidified slab. on the other hand,
If the Mg concentration exceeds 5 × (TO) +0.05, no matter how much metallic Mg is added, the refining function is saturated and no remarkable effect is exhibited, and the cost of metallic Mg increases. Problems occur. When the oxygen content (TO) has a margin with respect to the addition amount of metallic Mg, M
In some cases, gO and MgO.Al ₂ O ₃ are mixed. As a source of Al ₂ O ₃ , when molten steel 10 is smelted by a converter, an electric furnace, or vacuum secondary refining (not shown), it is mixed into molten steel 10 as a product of elution of refractories and deoxidation products. And
By using part or all of Al ₂ O ₃ , MgO
A spinel compound of Al ₂ O ₃ is formed. Also, the continuously cast slab 15 was magnified 5 times with a microscope,
FIG. 2 shows a sketch of the crystal structure in the range of 8 mm from the surface layer of FIG.
As shown in the figure, the crystal structure existing inside the chill crystal 20 solidified first by the primary cooling of the mold 13 also forms a fine equiaxed crystal 21, and the crystal structure is sufficiently refined. The equiaxed crystal 21 is also 8 mm or more from the surface layer.
Could be obtained. The steel sheet rolled using the slab 15 also had a fine crystal structure, and no ridging occurred in the pressed product. In addition, in order to increase Mg% of molten steel 10, metal M
In addition to the g particles, a Mg alloy such as a Si-Mg alloy or Ni-Mg can be used.

Further, the molten steel 1 in the tundish 11 is
0 was previously deoxidized by adding Al or an Al alloy, and then, as described above, with respect to the oxygen content (TO) of 0.0025% by weight, 3/8 × (TO) to 5 × (TO) +
0.0009-0.0625% by weight corresponding to 0.05 value
It is also possible to add particles of metallic Mg to the molten steel 10 in the tundish 11 so that the Mg content falls within the range of Mg%. Molten steel 1
By adding Al or Al alloy in advance and performing deoxidation, the oxygen content excessively contained in the converter, electric furnace, secondary refining (not shown), etc. can be appropriately reduced.
Inclusions such as Al ₂ O ₃ that do not act as inoculation nuclei can be reduced, and the corrosion resistance of the product can be improved and defects caused by the inclusions can be prevented.

[0011]

EXAMPLE Next, an example of a method for casting a ferritic stainless steel molten steel will be described. First, the molten steel was prepared by adding a chromium alloy in a converter or an electric furnace, decarbonizing and refining C to about 0.60% by weight, and then performing vacuum secondary refining. As a composition, C is 0.010 to 0.051.
% By weight, 0.33 to 0.40% by weight of Si, and 0.1% of Mn.
18 to 0.35% by weight, P is 0.010 to 0.029% by weight, S is 0.003 to 0.005% by weight, and chromium is 1%.
0 to 30% by weight, 0.001% by weight of Al, 0.0% by weight of N
072 to 0.0124% by weight; O from 0.0069 to
When the Al deoxidation containing 0.0084% by weight is not performed, the metal Mg particles are added into the tundish 11,
Mg% with respect to the oxygen content (TO) is 3/8 × (TO.
O) or more and 5 × (TO) +0.05 or less. The state of refinement (crystal grain size) of the crystal structure of the cast slab, the corrosion resistance after press working, and the ridging rank were examined (Examples Nos. 1 to 3 in Table 1). The evaluation of ridging was made based on the height of ridging (wrinkles) on the surface after 15% tensile deformation was applied to a JIS No. 5 tensile test piece prepared and mirror polished on the surface.
μm), rank B (less than 10 to 20 μm), and rank C (more than 20 μm).

First, in Example NO. 1 is T. O to 0.0
072% by weight and Mg% adjusted to 0.0028% by weight. A fine crystal structure having an average crystal grain size of 1.5 mm was obtained. The corrosion resistance after press working and the ridging generation rank were also A. The results were good, and the overall evaluation was good (○). Further, in Example NO. 2 and NO. 3 is
T. O is contained in 0.0069% by weight and 0.0084% by weight. In 2, it is 0.08
35% by weight, NO. No. 3 is a case where it was adjusted to 0.0056% by weight. 2 has an average crystal grain size of 0.7 m
m, NO. No. 3, a fine crystal structure having an average crystal grain size of 1.2 mm was obtained, and similarly, the corrosion resistance after press working and the ridging rank were good in A, and the overall evaluation was good (）). there were.

[0013]

[Table 1]

C is 0.010 to 0.051% by weight, Si is 0.33 to 0.40% by weight, and Mn is 0.18% by weight.
~ 0.35 wt%, P is 0.010-0.029 wt%, S is 0.003-0.005 wt%, and chromium is 10
-30% by weight, Al is 0.050-0.160% by weight,
In molten steel containing 0.0072 to 0.0124% by weight of N,
Deacidification was performed by adding T.l. O is 0.0023 to 0.0
In the case of 057% by weight, Mg% was adjusted to the above-mentioned range with respect to each oxygen content (TO), and the state of refinement of the crystal structure (crystal grain size) and the corrosion resistance after press working were determined. The ridging occurrence rank was investigated (Example N in Table 2).
O. 4-6). Example NO. 4 is Mg 60%
5% by weight, and the average crystal grain size is 1.
A fine crystal structure of 5 mm was obtained, the corrosion resistance after press working and the ridging rank were good in A, and the overall evaluation was good (（). Further, in Example NO.
No. 5, 0.0023% by weight of Mg%, NO. 6 is Mg
% Was adjusted to 0.0045% by weight.
No. 5 has an average crystal grain size of 0.7 mm and NO. In No. 6, a fine crystal structure having an average crystal grain size of 1.2 mm was obtained. Similarly, the corrosion resistance and ridging rank after pressing were A.
And the overall evaluation was good (良好).

[0015]

[Table 2]

On the other hand, as shown in Table 3, Mg%
Comparative Example NO. 1 and Mg%
Comparative Example NO. In 3,
Since the absolute amount of O is insufficient, the function of MgO as an inoculum nucleus is small, the average crystal grain size is 4.5 mm, and a coarse structure is formed. Ridging occurs during press working (rank C), and The gloss became poor, and the overall evaluation was poor (x). Further, in Comparative Example NO. In the case of 2, the metal Mg was added excessively and the Mg% was made too high, so that the corrosion resistance of the product was lowered,
Poor (x) result as overall evaluation.

[0017]

[Table 3]

Further, the molten steel is made to have the above-described composition conditions and metallic Mg.
Ingot casting was performed under the same addition conditions, and the solidified crystal structure of the slab and the occurrence of ridging after press working, surface gloss, etc. were investigated. The result was equivalent to the case.

The embodiments of the present invention have been described above.
The present invention is not limited to these embodiments, and all changes in conditions without departing from the gist are within the scope of the present invention. For example, as a method of adding metallic Mg or Mg alloy, a wire of metallic Mg or Mg alloy is used instead of granular material, or metallic Mg is added to molten steel in a ladle.
Alternatively, a Mg alloy may be added to increase Mg%.
Further, in the present embodiment, the method of rolling down the cast slab is used, but rolling can be performed without rolling down.

[0020]

According to the present invention, there is provided a method for casting ferritic stainless steel molten steel, comprising adding Mg or a Mg alloy to molten ferritic stainless steel containing 10 to 30% by weight of chromium. Mg% with respect to the oxygen content of the molten stainless steel is 3/8 × (TO) ≦
(Mg%) ≦ 5 × (TO) +0.05, so that the casting is refined and the rigging generated during secondary processing such as pressing is prevented, and the polishing is performed. And excellent surface gloss and corrosion resistance can be maintained without reducing the surface gloss.

In particular, in the method for casting ferritic stainless steel molten steel according to claim 2, since the ferritic stainless steel molten steel is deoxidized by Al or an Al alloy, an excessive oxygen content is suppressed and an oxide is mixed. Therefore, it is possible to prevent a decrease in corrosion resistance due to inclusion of a defect and an oxide due to inclusions due to inclusion.

[Brief description of the drawings]

FIG. 1 is a schematic view of a continuous casting apparatus used for a method for casting ferritic stainless steel molten steel according to an embodiment of the present invention.

FIG. 2 is a solidification structure diagram of a partial cross section of a slab.

FIG. 3 is a solidification structure diagram of a partial cross section of a conventional slab.

[Explanation of symbols]

Reference Signs List A continuous casting apparatus 10 ferritic stainless steel molten steel (molten steel) 11 tundish 12 immersion nozzle 13 mold 14 support segment 15 cast slab 16 rolling down segment 17 pinch roll 20 chill crystal 21 equiaxed crystal

Continuing from the front page (72) Inventor Yasuhiro Kinari 1-1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Masayuki Abe 1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka No. 1 New Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] 1. A molten Mg or Mg alloy is added to a ferritic stainless steel molten steel containing 10 to 30% by weight of chromium, and the Mg content relative to the oxygen content of the ferritic stainless steel molten steel is defined by the following formula (1). A method of casting molten ferritic stainless steel, characterized in that the casting is performed in the following manner. 3/8 × (TO) ≦ (Mg%) ≦ 5 × (TO) +0.05 (1) O is the total oxygen content in the molten ferritic stainless steel (% by weight) Mg% is the Mg content in the ferritic stainless steel molten steel (% by weight) 2. The ferritic stainless steel molten steel is Al.
2. The method for casting molten ferritic stainless steel according to claim 1, wherein the ferritic stainless steel is deoxidized by an Al alloy.